The present invention relates to an automatic transmission, and more particularly, to an improved shift control method and system to decrease shift shock.
Generally, an automatic transmission determines a target speed on the basis of a shift map using vehicle speed and throttle open angle as parameters, and performs hydraulic pressure duty control in order to operate specific engaging members within the transmission. Gear shifting is thus automatically performed.
However, if a significant number of shift signals are continuously generated, for example, due to frequent depressions of the accelerator pedal in a short time period, a new shift signal is generated before a shift according to a previous shift signal has been terminated. In this circumstance, shift operation according to the previous shift signal stops and a new shift operation according to the new shift signal is performed. Consequently, frequent changes of the target speed in the automatic transmission cause the hydraulic pressure to be incorrectly routed so that shift shock occurs.
In a preferred embodiment of the present invention, the shift control method includes generating a first shift signal for shifting to a target shift speed, detecting a shift signal generated within a predetermined period after the generation of the first shift signal, and determining if the number of shift signals generated is greater than or equal to a predetermined number, withholding synchronization according to the current shift signal, and determining if synchronization according to a previous shift signal has been terminated, if it is determined that the number of the shift signals generated is greater than or equal to the predetermined number, and performing synchronization according to the current shift signal after the synchronization according to the previous shift signal has been terminated.
In a preferred embodiment, the shift control method further comprises performing the synchronization according to the current shift signal if the number of shift signals generated is smaller than the predetermined number. It is also preferable that the predetermined number is three, and the predetermined period is determined based on a target speed determination history of the shift signals generated before the current shift signal.
In another preferred embodiment of the present invention, a shift control system for an automatic transmission comprises plural sensors and an appropriately programmed control unit. More specifically, a vehicle speed sensor detects vehicle speed and outputs a corresponding signal. A throttle position sensor detects the open angle of the throttle valve and outputs a corresponding signal. The transmission control unit determines a target speed on the basis of signals input from the vehicle speed sensor and the throttle position sensor, and generates a corresponding shift signal. Preferably, the transmission control unit is programmed with various instructions for shifting control. These instructions may include instructions for generating a first shift signal for shifting to a target shift speed, instructions for detecting a shift signal generated within a predetermined period from the generation of the first shift signal and determining if a number of shift signals generated is greater than or equal to a predetermined number, instructions for withholding synchronization according to the current shift signal and determining if synchronization according to a previous shift signal has been terminated if it is determined that the number of the shift signals generated is greater than or equal to the predetermined number, and instructions for performing synchronization according to the current shift signal after the synchronization according to the previous shift signal has been terminated.